Density functional study of oxygen adsorption on 4-Å carbon nanotubes

Adsorptions of both oxygen atoms and oxygen molecules on 4 Å single-wall carbon nanotubes, which have been fabricated using a templating method recently, are studied by the plane-wave pseudopotential method. Our calculations will provide some useful information on the stability of such ultrasmall tubes under ambient environment. We found that the calculated oxygen binding energy shows strong chirality dependence. Different adsorption pictures of singlet ${\mathrm{O}}_2$ can be used to select a single chirality from these ultrasmall-radius tubes.

Figure 1

(Color online) Ball-and-stick model (before relaxations) of a single O atom adsorbed on tube (5,0) at site I (top, left), tube (5,0) at site II (top, right), tube (3,3) at site I (middle, left), tube (3,3) at site II (middle, right), tube (4,2) at site I (bottom, left), and tube (4,2) at site II (bottom, right).

Figure 2

Energy band structures of tubes adsorbed with one O atom for (5,0), (3,3), and (4,2), with nominal formulas ${\mathrm{C}}_{20}\mathrm{O}$, ${\mathrm{C}}_{24}\mathrm{O}$, and ${\mathrm{C}}_{56}\mathrm{O}$, respectively. The band structures of pristine tubes are also shown for comparison. Note that the supercell contains two primitive cells in the case of tube (3,3). The Fermi level is at 0 eV.

Figure 3

(Color online) Top and side views of an ${\mathrm{O}}_2$ molecule chemisorbed on tube (5,0): (a) site I, (b) cyclo-addition, and (c) epoxy structure.

Figure 4

(Color online) Top and side views of an ${\mathrm{O}}_2$ molecule chemisorbed on tube (3,3): (a) cyclo-addition, (b) site II, and (c) epoxy structure.